1. Field of the Invention
This invention relates to the detection of a member interrupting one or more beams transmitted between an emitter and an associated detector in an irradiated field, and more particularly relates to touch input detection systems for determining the intrusion and the relative position of a stylus within an irradiated field generally adjacent to an electronic display and formed by a plurality of infrared emitter/detector pairs.
2. Description of the Prior Art
Detection systems comprising a plurality of light emitting and detecting pairs located around the periphery of an irradiated field have been employed in a number of applications. For example, infrared detector fields can be used as a safety interlock or an anti-intrusion system for preventing access to a certain area or as a safety barrier around a machine. One ever increasing use of such systems is as a touch input device to an electronic display. For example, an array of infrared light emitters and detectors can be positioned around the periphery of an electronic display such as a CRT or a flat panel display. A number of such systems employ an X-Y matrix of emitters and detectors with associated emitters and detectors being axially aligned in pairs. In such touch entry systems, the introduction of a stylus within the irradiated field in proximity to a portion of the display permits input for controlling the operation of a computer communicating with the electronic display and the touch input apparatus. Conventional infrared or light "type" touch input devices employ opto-devices such as LEDs, photodiodes, and phototransistors. An example of a touch input system utilizing opto matrix frames consisting of infrared emitters and detectors may be found in U.S. Pat. No. 4,267,443, "Photoelectronic Input Apparatus", issued on May 12, 1981.
The arrays of emitters and detectors commonly used in conventional opto matrix touch input systems are normally positioned on a peripheral frame comprising a printed circuit board which has a central opening. The printed circuit board can be positioned within the bezel on a conventional CRT screen with the central opening aligned with the visual display surface. The arrays of emitters and detectors can be arranged in a curved pattern to correspond to the contour of a curved CRT screen or can be positioned within the same plane for use with flat panel displays. In either instance, the opto-devices may be mounted perpendicular to the printed circuit boards. Such an arrangement, however, requires planar members on which the opto-devices are mounted to extend perpendicular to the display surfaces in the manner disclosed in U.S. Pat. No. 4,267,443 and U.S. Pat. No. 4,591,710. This configuration, however, results in a comparatively high profile opto matrix frame, especially for flat panel opto matrix frames. An alternative approach orients the opto matrix devices on brackets mounted on the peripheral printed circuit board frame, with the light emitting devices adapted to emit a beam extending generally parallel to the plane of the flat printed circuit boards. This manner of mounting the opto matrix devices is considered conventional and corresponds to the manner in which individual or a small number of light emitting devices are normally positioned on a printed circuit board. Examples of this conventional mounting technique for discrete light emitting devices are shown in U.S. Pat. No. 3,335,387; U.S. Pat. No. 4,065,198; and U.S. Pat. No. 4,534,604.